1. Field of the Invention
The present invention relates to a substrate holding device that holds a substrate, such as a wafer, during semiconductor fabrication and, in particular, a substrate holding device included in an exposure system for fabricating a semiconductor device.
2. Description of the Related Art
An exposure system used in fabrication of a semiconductor device or a liquid crystal display device includes a substrate holding device that holds an original plate, such as a mask or a reticle, and a substrate, such as a semiconductor wafer or a glass substrate, which is an object to be exposed (hereinafter simply referred to as “a substrate”).
Japanese Patent Laid-Open No. JP2001-044093 discloses an example of such a known substrate holding device. In general, a wafer transferred to a stage is coarsely pre-positioned, and is thereafter fine positioned. In the above-described publication, a wafer is transferred to a wafer chuck after pre-alignment, and deviation from a reference alignment mark is calculated. If the resultant correction value of the wafer exceeds a maximum operating distance of a XYθ stage, the XYθ stage is moved to the maximum position, and the wafer is then transferred from the wafer chuck to a wafer receiving chuck (hereinafter referred to as “pins”). The XYθ stage moves back to the original position, and the wafer is then transferred back from the pins to the wafer chuck. This operation is repeated until the position of the wafer is corrected.
This substrate holding device, in which a wafer is transferred from the wafer chuck to the pins for every alignment correction of a deviation of the wafer, must wait until the wafer is released from the wafer chuck, since the wafer chuck always holds the wafer as tightly as it does during exposure. Also, if the pins strongly push up the wafer in order to reduce the waiting time, there is a possibility of the wafer being considerably offset from the proper position.